Baby it’s cold outside!

Ok, so the air has been brutally hot and humid since mid June. We have set records in the northeast for rainfall. This has all been due to a combination of the clockwise rotation of the Bermuda High to our east and an upper level counter clockwise rotating low to our west with us right in the middle getting strong SW winds for weeks.

courtesy ABC6 Philadelphia

Ironically, all this hot weather brings very cold water to the beach. How? Surface ocean water actually flows 90 degrees to the right of the wind direction in the northern hemisphere thanks to something called Ekman transport (http://en.wikipedia.org/wiki/Ekman_transport). So when the wind blows from the southwest, the surface water moves southeast away from shore, and cold bottom water moves inshore from the ocean floor and rises to the beaches. Somewhat like a conveyer belt movement.

The map below  is of ocean currents along the northeast US coastline. It shows the average currents over a 25 hour period late July 8th into the 9th. Notice that all the surface water is moving offshore. This is the top of the conveyor belt of currents mentioned earlier. The only thing replacing all that water along the coast is the cold, murky bottom waters being pulled in from offshore.

This circulation results in VERY cold water up on the beach, and a miserable beach weekend if you want to go in the water. The NJ coast south of Asbury Park and Maryland beaches seem to be bearing the brunt of the cold water, though the upwelling stretches all the way south to Kitty Hawk, NC. This is shown quite clearly in the sea surface temperature (SST) image from Rutgers below. Lifeguards in Long Beach Island NJ reported July 4 weekend ocean temperatures in the upper 50s. Brrrrrr……

Below are wind roses from WeatherFlow that show the dominant direction the wind came from between June 15-July 9 2012 (left) and 2013(right) at Tuckerton, NJ. Not only were winds dominantly from the southwest this year, but there were little to no winds from the north, northwest or northeast that would counteract the upwelling. As long as winds continue from the southwest, the cold water will continue to remain at the beaches.

One other note about the upwelled water. The bottom water brings nutrients to the surface from the ocean floor. Translation: anything that died or that fish pooped on the ocean floor is now pushed up to the surface and to the beach. This makes for very green, murky water that is filled with, well, nutrients. Phyptoplankton, which are the tiny plants in the ocean that are the base of the food chain, love the nutrients (fertilizer) and start to bloom. This satellite image from the University of Delaware shows an enormous but weak bloom far off the NJ coast on July 6. We will be keeping an eye on this bloom in the coming weeks to months.